Gypsum wallboard is a common building material used in new construction and renovations to define and cover interior wall surfaces. Drywall or sheetrock, as gypsum wallboard is sometimes called, comprises a calcined gypsum core sandwiched between two layers of heavy paper. Wallboard is cut during installation to fit door and window casings, shelves, and stairways leaving odd sized pieces of scrap board. Wallboard waste is also generated during renovation and demolition. The cost of disposing of this waste and scrap board is ever increasing. Rising landfill fees reduce the profit margin for contractors and landfill space is becoming more scarce.
Calcium sulfate (CaSO.sub.4), gypsum, the core of wallboard, has many uses. The mineral is used as a fluxing agent, a retarder in portland cement and a filler in paper and textiles. Ground gypsum wallboard can be used also as a component of recycled wallboard, and as blow-in insulating material. Gypsum is a natural fertilizer and reclaimed gypsum can be pelletized for use in agriculture and landscaping. Therefore, reclaiming the gypsum from scrap wallboard and recycling its components not only reduces the burden on landfills and reduces contractor dumping costs but can produce profitable new products.
Attempts to reclaim wallboard components have included using machines which tumble wallboard pieces in a large barrel containing free weights. See U.S. Pat. No. 5,183,213. The weights crush the wallboard into small pieces within the barrel releasing the gypsum from the paper. The contents of the barrel are then emptied onto a vibrating conveyor where the gypsum is separated from the paper. U.S. Pat. No. 5,238,195 describes a process by which reclaimed gypsum is added to clean gypsum and treated to produce a partially recycled wallboard core. U.S. Pat. No. 5,304,276 describes an apparatus that strips the paper from the core of the wallboard leaving the gypsum core intact to be discarded or recycled. A set of rollers crush the gypsum interface holding the paper to the core. The paper is collected in sheets and the core remains substantially intact. A shredder having a punch and die roller system to dispose of wallboard rejects generated during manufacture is described in U.S. Pat. No. 4,801,101. In European Patent Application No. 0 386 998 A1, wallboard pieces are pulverized by a hammermill releasing the paper from the gypsum. The paper and gypsum particles exit the hammermill through holes in the hammermill grate and are then separated by a series of screens. Incomplete separation of the paper from the gypsum can occur however because the paper can be torn into extremely small pieces by the hammermill and is able to pass through the screens.
Improved machines and methods for creating useable by-products of gypsum wallboard and separating reclaimed gypsum from free paper in recycled wallboard are needed. A wallboard recycling apparatus that can handle odd sized pieces of scrap board, preferably in bulk quantities, and which utilizes a single operator would increase not only the profit margin of the reclamation process but increase the profit margin of sheetrock contractors and encourage wallboard recycling.